Oxidation inhibitor



Patented on. 21, 1941 OXIDATION INHIBITOR Roger W. Richardson,-Westfield, N. J assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application July 30, 1938,

- Serial No. 222,147

' 11 Claims.

This application relates to improved oxidation inhibitors, their preparation, and their use in mineral oils, particularly refined lubricating oil.

It relates more particularly to the preparation of improved hydroxy aryl sulfide oxidation in,- hibitors, by an electrical polymerization treatment, the improvement being marked mainly by increased efiicacy of the thus'treated compounds when contained in the oils for overcoming sludging even when subjected to oxidation over prolonged periods and in being satisfactorily. noncorrosive. i .In previous work it was found that phenolic sulfide and similar hydroxy arylfoxidation inhibitors, while highly effective in-improving the engine performance of an oil in. accordance with their ability to lower the oxidation absorption rate and to increase the lead tolerance of the oil,

' acted objectionably to some extent by increasing sludge formation, especially at low temperatures,

and copper strip corrosion, especially when used in more highly effective concentrations. With a view to reducing this corro'siveness and sludging, a voltolization treatment of these compounds was tried. Not only were the results gratifying in so far as these objectives were attained, but at the same time the 'voltolized products were found to improve the service performance of oils in actual engine tests remarkably well. Allthe factors of the improvement are difiicult to determine, but at least in addition to the more satisfactory sludge and copper strip corrosion tests, the oils containing the voltolized inhibitors showed an improved lead tolerance. Each of these tests is described in connection with the tabulated resultswhich demonstrate the superiority of the voltolizedinhibitors.

For'some time it has been recognized that it is difficult to refine a viscous mineral oil without rendering the oil more susceptible'to oxidation, and it has been a common practice to add relatively small quantities of compounds known as oxidation inhibitors to refined oils to inhibit the oxidation. Careful studies of efiects these inhibitors have on the oils have'revealed that the advantage gained in inhibiting oxidation by addition of these agents to an oil mightbe at the expense of some detrimental effects they induce. For example, among compoundsfound toenhance the qualities of lubricating oils by lowering the oxidation, absorption ratelof the oil and to perform this function meritoriously without precipi tating sludge under. engine performance condi tions; some have-been found to behave adversely in making the oil'show increased copper strip corrosion tendencies and increased 'sludging tendencies under prolonged oxidation, while some act unfavorably in other oxidation tests. Among the compounds which perform notably well in reducing the oxidation absorption. rate and improving engine performance of oils are the recently developed phenolic-sulfides, having good oil solubilities, in particular the alkyl phenol thio-ethers and alkyl phenol disulfides. f The general structures of these compounds can be graphicallyrepresented as follows: 1

in which R is a hydrocarbon group, S is an atom of sulfur or a related metalloid taken 1 or several times (93:1, .r=-2, etc.) and R is an aromatic nuclear group. At least one sulfur atom is linked between the hydrocarbon groups as in a thioether or a disulfide. The sulfur atoms may be wholly or partly replaced by a related metalloid, e. g., selenium or tellurium which are members of the sulfur family in Group VI of Mendeleeffs Periodic Table of Elements. The aromatic nuclear group R is linked to a hydroxyl group,

-OH, and also preferably to at least one alkyl group of about 4 to 6 carbon atoms. The other hydrocarbon group R, maybe a similar aromatic group with or without substituted groups or a short chain aliphatic group of about 2 to 8 carbon atoms. As examples of the type of sub stances intended, the following structural formulae are presented. It will be understood that the substances depicted are merely illustrations and that this list could be considerably extended,

but in all cases there appears in the compound a metalloid atom, e. g., a sulfur atom connected 7 to at least one aromaticnucleus which has a substituted' hydroxyl group and preferably in addition a substituted alkyl group.

OH OH moi-s om moi-some.

CxHz C1111 HO OH BIC-380E These phenolic sulfides may contain other substituent groups in addition to a hydroxy and an alkyl group, providing the additional substituent groups do not; substantially impair .the effectiveness of the compoundas an oxidation inhibitor nor offset the solubilizing effect of the alkyl groups. Examples of suitable groups or radicals which may be attached to the aryl or alkyl groups are: alkyl and aryl radicals, halogens, and such radicals asacyl, additional hydroxyls, carboxyl, amino, nitro, etc.

Phenolic sulfides which are used in this invention for improvement by voltolization may be prepared by the reaction of phenolsor phenol sulfides with reagents such as sulfur chlorides, or carbon disulfide, preferably the former. Elementary sulfur or reactants furnishing sulfur may be used at high temperatures. The reaction with carbon disulflde is carried out at low tem-,

peratures. The reaction with the sulfur chloride is conducted in the presence of aninertdiluent,

preferably an alkyl halide, such as dichlor-,,

ethane, which boils at the reaction temperature and is refluxed into the reaction zone. Suitable alkyl phenols for use may be obtainedby condensing phenols with olefins of preferably 2 to 8 carbon atoms. The reaction of the phenol with sulfur chloride is carried out at temperatures of about 60 to 140 C. and preferably of about 80 to 110 C. In comparison with the other sulfiding. reagents, sulfur chlorides increase the yields of desired products. Yields as high as 92.1% of light yellow crystalline amyl phenolic sulfide have been recovered by this preferred method. The sulfur chloride used is preferably of high purity although commercial grades may be used. The sulfur chlorides, i. e., the mono and the dichloride, may be used individually or mixed, and in a proportion of about 0.1 to 1.5 mols per mol of phenol. They may be replaced by other suitable halide reagents, for example selenium oxychloride (SeOClz). Higher polymers which appear to have a structure characterized by a string of alkyl hydroxy phenyl radicals interlinked by sulfur atoms, are obtained in larger amounts by using the higherratios of sulfur chloride to phenol and by lengthening the reaction time. Higher sulfides are obtained by using more of the monochloride of sulfur.

These compounds when subjected to silent electric treatment alone or dissolved in high concentration in suitable oils, preferably in concentrations of 20 to 50% by weight, result in products which have been found to be as effective in their oxidation characteristics as the original compounds, and which are improved in their diminished sludging and copperstrip corrosion tendencies.

The process of voltolization consists in subjecting the material to the action of high tension silent electric or glow discharges, preferably of an alternating current. The treatment is generally carried out under vacuum. The pressure may be varied from .001 to .01 atmosphere, .1, .5, or even as high as .8 atmosphere. The voltage used is preferably in the range of 4000' to 10,000

volts, although higher voltages may be used,

especially when good dielectrics are available. The frequency may be as low as 60 cycles and as high as 1,200, 10,000 or more cycles.

In the usual treatment, the temperature during the treatment with silent electric discharges is maintained at about room temperature or substantially thereabove to give the material suitable fluidity without undesired decomposition.

Cooling means' are used to prevent excessive rises of temperature.

Well known types of apparatus may be used in the present process for the electrical treatment, such as the usual tube and trommel designs. The tube type of apparatus comprises a vertical tube preferably constructed of a dielectric material such as glass coated on the outside with a conductor electrode, a central electrode disposed in the center of this tube, provision being made for a high tension silent electric discharge between the electrodes. The trommel type of apparatus comprises a series of insulated plates spaced a few millimeters apart and mounted on a rotatable shaft, the entire shaft with its plates being disposed within a horizontal drum maintained approximately half full of the material to be voltolized. The bottom portions of the plates dip-into the material to be voltolized and as the'shaft rotates the material drips down over the surface of the plates to form a film thereon. The high tension silent discharge occurs between the plates.

The phenolic sulfides voltolized according to the present invention may be in a purified or crude state, and preferably concentrated in a high boilin carbonaceous material, e. g. petroleum, dewaxed oils, voltolized oil, chemically refined oils, oils obtained by solvent extraction, fatty oils, such as, rape seed ofl, petroleum wax, ester waxes, or mixtures of such materials, so that the mixture contains 15 to 75%, and preferably 20 to 50% by weight of the phenolic sulfide.

The phenolic sulfide may be partially voltolized and then blended with the other materials indicated. The voltolization treatment may also be carried out in the presence of such gases as hydrogen, carbon oxides, nitrogen, gaseous hydrocarbons, and the like. It may also be carried out in the presence of sulfur, hydrogen sulfide, sulfur halides, halogens, selenium, boron fluoride, and the like. The presence of small amounts of sulfur, in the elementary form during the voltolization is considered to be particularly useful in producing an antioxidant which makes an exceptional increase in lead tolerance of an oil.

The products obtained by the voltolization of the phenolic sulfides, according to the voltolization method described, will be found to contain materials having higher molecular weight than the starting material, but the voltolization is desirably controlled to limit the extent of increase of molecular weight and viscosity to avoid the formation of products insoluble in mineral oils: In general, the degree of improvement V varies in proportion to the extent of voltolization which canbe measured by the energy-input. The use of 20 to 30 kwh. per gallon of material treated was found togive satisfactory results but lower and higher amounts such as'5, 10, 40, and 50 kwh. may be used. The high molecular weight productsmay be separated'by extraction or distillation. Effects vof voltolization on organic compounds of the type treated denote that the.

phenolic sulfides, in addition to being polymerized, are probably rendered unsaturated by the silent electric discharge; become alkylated by reaction with associated hydrocarbons, fatty oils, etc. objects of this invention will be apparent, from the following description and claims.

Other and further in dichlorethane is then added slowly with stirring to the boiling solution'of amylphenol. The hydrogen chloride gas evolved duringthe reaction is withdrawnfrom the reaction zone through the reflux condenser. When the addition of sulfur monochloride solution is completed, the boiling of the reaction mixture under reflux is continued for about sixhours or until no further effusion of hydrogen chloride occurs. The time They are believed to The oxidation inhibitors prepared accordingv I to this invention effectively stabilize mineral lubricating oils under service conditions, especially highly refined oils, e. g., oils refined by chemical purification, solvent extraction by selective solvents suchas flphenol, furfural, sulfur dioxide, nitro--benzene, crotonaldehyde,'propane, etc. used alone or in mixtures such as propanecresohsulfur dioxide-benzene, etc., clay and/or acid treating, aluminum chloride treating, voltolizing, hydrogenating, etc. Various types of refined viscous oils, such as white oils, greases, turbine oils, synthetic oils, etc., and especially those ,oils having viscosity indices of 60, 80, 100 or higher are stabilized by these oxidation inhibitors. These inhibitors are beneficial in lubricat ing'oils having viscosities suitable for motor lubrication, e. g., a viscosity of at least 35 Saybolt seconds at 210 F., and which are only in' a 1 partly refined form, as by steps of distilling, de-

waxing, treating with chemical agents including adsorptive materials, they crude stocks being pale oils, neutrals, bright, or" cylinder stocks derived from mineral oils, or other carbonaceous materials.

The lubricants to which the improved oxidation inhibitors. of this invention are added may also contain dyes, soaps, pourinhibitors, added sludge dispersers, other oxidation inhibitors, thickeners, viscosity index improvers such as soluble polymers, oiliness agents, fatty oils as ,suchor treated by heat thickening, voltolizing, sulfurizing, etc., extreme pressure lubricating agents, colloidal solids such as graphite, etc., and

be blended with other oils, fats, or waxes, treated or untreated.

The improved oxidation inhibitor may be used in any suitable concentration for'improving the described types of oils. The amount which may be used is in the range of .01 to 5% of the total composition but .04 to 20% is generally suflicient.

The following examples and tests illustrate the preparation and use of the voltolized compounds described herein as stabilizing agents in lubricating oils.

EXAMPLE I of refluxing can be cut down by blowing an inert gas, suchas nitrogen or flue gas through the reaction mixture. This may be done during the reaction orafter all the reagents have been added as desired.

The solvent dichlorethane may, be removed from the reaction mixture by distillation and any unreacted amyl phenol may then be removed by distillation under vacuum at a temperature of preferably. not above about 150 to 175C.

There is thus obtained asdistillation residue a product consisting substantially of the desired amyl phenol disulfide which may be represented as having a general structure:

Other configurations may result depending upon the initial configuration of the alkyl phenol.

- This product is a dark brownto reddish colored viscous liquid, which is soluble in most organic solvents, including petroleum and fractions thereof such as gasoline, kerosene, burning and Diesel oils, and lubricating oils. The crude" product may be used directly as obtained or after any desired purification, as by treatment with selec- One molal proportion of tertiary amyl phenol is dissolved in dichlorethane, known also as ethylene dichloride (CHzClCHzCl), and the solution is heated to boiling under reflux. A solution of A; molal proportion of sulfur monochloride tive solvents or adsorptive materials such as clay. The tertiary amyl phenol disulfide may be-employed' in this crude condition directly asobtained or after purification to .act as an oxidation inhibitor, but this product is further improved by the succeeding steps. 1 Y

I A solution is made up in weight percentages of 60% mineral lubricating oil and 40% of refined tertiary amyl phenol disulfide prepared as indicated and this solution is treated in a glass voltolization tube under an absolute pressure of about 5 to 10 mm. (mercury gauge) with a silent electric glow discharge at about 7,000 volts and 1,000 cycles/sec. frequency for a time until the power consumption has reached about 25 This voltolized product containing kWh/gal. about 40% of voltolized tertiary amyl phenol disulfide when added in very low concentrations of about .1 to 2%to a refined lubricating oil effectively acts as an oxidation inhibitor while permitting the oil to pass the corrosion test and makes the oil give excellent engine performance.

Tests under comparable conditions were made 1 ma C. F. R. (Cooperative Fuel'Research) engine to determine the efficacy of this voltolized product for improving the engine performance of a highly refined lubricating oil having a relatively high oxidation susceptibility. These tests are exemplified by a set of runs made on the following samples; (1) A highly refined lubricating oilwith no added oxidation inhibitor,-run as a reference oil; (2) A blend of the reference oil with a voltolized concentrate of amyl phenol disulfide inbil,

the voltolized concentrate, containing 40% by weight of voltolized amyl phenol disulfide, being prepared asdescribed in the foregoing example and added to the ref erence oil in an amount making 0.63% by weight of the blend, thus making a con- These samples were submitted to the following tests under comparable conditions and the results are shown in the following table:

Corrosion test This consists in immersing a bright copper strip for 3 hours in the oil maintained at 212 F. to determine the presence of corrosive sulfur in the oil as indicated by discoloration and pitting of the copper.

Lead tolerance test This test is used to determine the tendency of an oil to corrode bearings. It is also known as the Underwood test. 1500-00. of the oil is maintained at 325 F. and is sprayed for 5 hours C. F. R. engine tests Demerits Sample tested {33. f Piston I Degree Carbon Overalldep. overstickunder nish Tg f all ing piston skirt 23 F. 1 Reference oil 390 5.00 3 855 5 5 100 2 Reference oil+0.25% voltolized amyl phenol disulfide. 390 1.42 0 0 3 2 28 Such results plainly show that the added volagainst two sets of bearings, each having coptolized oxidation inhibitor made the refined oil per-lead and cadmium-silver alloy halves. The give an excellent engine performance, especially 30 oil dripping from the bearing is recirculated. in preventing ring sticking. This performance The bearings are weighed before and after the of the voltolized inhibitor compares favorably test to determine any loss in weight. The test is with the non-voltolized inhibitor. then repeated with addition of a soluble lead The use of the voltolized amyl phenol disulfide compound, preferably lead oleate. in increments oxidation inhibitors was found to be particularly of 0.005% by weight of lead xid A l in advantageous over the unvoltolized compound of weight of 50 mg. or more in the cadmium-silver this type from the standpoint of copper strip bearing halves indicates the lead tolerance of corrosion which was investigated by the conventhe oil has been exceeded, and the amount of tionally'adopted laboratory test briefly described lead computed as per cent lead oxide, added in herewith in which blends of refined lubricating 40 the previous test is recorded as the lead toleroil with voltolized inhibitor and with unvoltolized ance. A lead tolerance below 0.020 is considered inhibitor having substantially the same lead tolunsatisfactory. erance were compared.

The samples prepared for these tests consisted Dynamic Omdatwn sludgmg test of; In this test, procedure outlined in the J S. A. E. (a) Refined mineral lubricating oil containing Of 1934, VOL P e 167 and known as the no added inhibitor as a reference oil; Indiana life test is largely followed. Air is (b) The reference oil blended with non-voltolblown at t e ate of 10 liters per hour throu ized amyl phenol disulfide concentrate 300 ml. of oil in a Pyrex boilin e aintained containing 40% by weight f non-voltolat 341 F. At the ends of consecutive 24 hour ized amyl phenol disulfide, prepared as deperiods, samples of the oil are removed and the scribed in Example I, the blends containamount of material insoluble in A. S. T. M. preing 0.25%, 0.50%, and 1.00% of this noncipitation naphtha is determined and recorded voltolized concentrate; in mg. per 10 g. of the oil sample tested. This (0) The reference oil blended with a voltolized test permits the progressive deterioration of an oxidation inhibitor concentrate containing oil over a prolonged period of oxidation to be ob- 40% by weight of voltolized amyl phenol served. The life of the oil is considered as the disulfide prepared as described in Examnumber of hours which the oil sustains this oxiple I, the blends containing 0.25%, 0.50%, dationtreatment before 10 mg. of the naphtha and 1.00% of this voltolized concentrate. insoluble sludge per 10 g. of oil is formed.

Corrosion, sludging, and lead tolerance characteristics Dynamic Pfirgent 1midiation Lem in i itor s u 2 n2: s- Sample concenggygfg agg sludge/l0 g. g

trate in oil in consecto g blend utive 24 hr.

periods a Reference oil 0.00 Pass 0, 0,0 0, 20 0.010 b Reference oil+ 0.25 Does not pass 0,0,0 140 0. 030

Non-voltolizedvnuu.. L 0.50 do Amy phenol disulfide concentrate. 1.00 U. 0 Reference oil+ 0.25 Pass 0,0,0, 0, 0. 35

voltolized amyl 0 50 do l Phenol disulfide concentrate 1.00 .do

'These datavindicate that the voltolization makes the amyl phenol disulfide much more satisfactory from the standpoint of copper strip corrosion avoidance and lowering of sludging under the dynamic oxidation test without dimin-- ishing its lead tolerance improvements. The

"life of the lubricating Oil when blended with the voltolized inhibitor is about 24 hours longer than when blended with non voltolizedjinhlbitor.

' Theeflect of voltolization on a phenolic sulfide oxidation inhibitor of the type in which correction of increased sludge formation rather than acorrosion tendency constitutes a problem is demonstrated by comparative tests "on a phenolic sulfide which has a lower sulfur, content than the disulfides, for example, on tertiary amyl phen61 sulfide, as 'shown in the follwoing example:

I EXAMPLE .lI 1 By s'ub s titut ing sulfur dichloride in the process described in Example I for the sulfur monochlo- .ride, instead of the phenolic sulfide with a disulfide llnkagea phenolic sulfide with a thin-ether linkageis produced. It was found that the nonvoltolized phenolic sulfide thus prepared when used as an oxidation inhibitor in some refined light lubricating oils caused an increased sludge formation, but when this phenolic sulfide was voltolized in a manner described, this sludging tendency was. reduced considerably.

@portion of tertiary amyl phenol sulfide, pre-.

paredgin accordance with the method described,

' f waeyoltolized-to a viscosity of 4,000 seconds Sayblfi at 210 vF. in a glass tube apparatus using conditions similar to those set forth in Example I, the power consumption being above 20 kwh. per gallon.

(1) Samples were prepared of a refined light I 'mineral lubricating oil containing no added oxidation inhibitor, to be used as a reference oil, and 3 (2) A blend of the refereneeoil with .2% of the voltolized tertiary amyl phenol sulfide, prepared in accor lance with Example II. v

These samples were subjected to the'following tests:

Corrosion test The copper strip test previously described.

Oxidation rate test This consists in measuring the number of cc.

of oxygen absorbed by cc. of an oil .per J minute intervals at 200 C. Y

Slick test I This consists in maintaining 10 g. of the sample in a flask with oxygen atatmospheric pressure and 200 C. for 24 hours, cooling the thus treated oil, diluting with naphtha, filtering and weighing the precipitate formed after the mixture has stood one hour at 25 C. The Sligh number is expressed as the milligrams of precipitated sludge formed. This method follows the test described in the .A.- L. Proc. .A. S. T. M. 2'?

Cone deposit This test determines the tendency of an oil to deposit solid matter upon a heated metallic conical surface, an oil sample of 60 cc. being slowly run in 2 hours over this surface maintained at 250 C., and the grams of deposit washed free of oil being determined.

The results or thesetests v are shown in the following table: I

Copper Oxidation C Sample strip corrate cc./l5 o rosion min. depositg Refined light lubricat- Passes; 112-95 8.9 I 0. 42v Rli g Oil (refereficleooil I eerence o 4 voltolized tertiary }--do 2.6 3 0.16 amyl phenol sulfide.

These data show that an excellent non-sludging 'oxi'dation'inhibitor is made by voltolizing the amyl phenol sulfide, the oxidation'rate of" the refined'oil being efiectively lowered from anabsorption of about 95 cc. of oxygen per 15 minutes to" an absorption of about 24 cc. per 15 minutes,

while the sludging as indicatedby the Sligh test and cone-deposit was considerably reducedwhen the refined oil was blended with 0.2% ofv the voltolized amyl phenol sulfide. The non-voltolized amyl phenol sulfide blended with light lubricating oils ordinarily fails to respond as well in all of these tests.

The tabulated facts from the various tests,

- such as those illustrated, lead definitely to the conclusion that voltolization of the hydroxy aryl sulfides is highly beneficial in eliminating certain objectionable characteristics which they maypossess without impairing their eflicacy as oxidation inhibitors. Additionally, it is believed that the voltolization further improves these compounds for use as oxidation inhibitors and other purposes, besides thosealready mentioned,

for example, by increasing their oil solubility in some instances, in lowering their volatility so as to reduce their loss by vaporization, and by imparting pour inhibiting and sludge dispersing,

properties to them.

This invention is not limited to any specific example or theories, all of which have been presented solely for the purpose of illustration, but is to be limited only by the following claims in which it is desired to claim all novelty in so far as the prior art permits.

l. A process for the production of an improved lubricating oil oxidation inhibitor from a hydroxy aryl compound containing a chemically combined sulfur family metalloid selected from the class consisting of sulfur and selenium attached to an aryl nucleus and interlinking hydrocarbon groups in said compound, which comprises subjecting said compound-to the action of a silent electric discharge at an intensity and for a period sufilcient to decrease sludging and corrosion tendencies of the compound materially when blended with a refined lubricating oil to increase the stability of the oil.

2. A process for the production of an improved oxidation inhibitor from a hydroxy aryl compound containing a combined metalloid selected from the class consisting of sulfur and selenium attached to an aryl nucleus and interlinking hydrocarbon groups in said compound, which comprises voltolizing a mixture of the hydroxy aryl compound and a high boiling carbonaceous material selected from the class of fatty oils, hydrocarbon oils, fats, and waxes, said mixture containing 15 to 75% by weight of the hydroxy aryl compound, and continuing the voltolizing until said mixture is converted into a product having substantially increased sludge dispersing and corrosion inhibiting properties.

3. A process in accordance with claim 2, in which the high boiling carbonaceous material is a petroleum wax.

4. A process in accordance with claim 2, in which the high boiling carbonaceous material is rapeseed oil.

5. A process in accordance with claim 2, in which the high boiling carbonaceous material is a hydrocarbon lubricating oil.

6. Process for the production of improved phenolic sulfide, capable of efiectively lowering the susceptibility of refined mineral oils to degradation by oxidation, comprising subjecting said phenolic sulfide to the action of a silent electric discharge at an intensity and 'for a period sufficient to decrease sludging and corrosion tendencies of the compound materially when used as an oxidation inhibitor in a refined mineral lubricating oil.

'7. Process as described in claim 6, in which the phenolic sulfide subjected to the action of a silent electric discharge is an alkyl phenol sulfide.

8. Process as described in claim 6, in which the phenolic sulfide subjected to the action of a silent electric discharge is a disulfide.

9. An improved phenolic disulfide polymer addition agent for lubricating oils consisting essentially of a phenolic disulfide electrically poly- ROGER W. RICHARDSON. 

